1. Field of the Invention
The present invention relates to a method of connecting a terminal to a wire, in which a wire connection portion of the open barrel-type terminal is pressed over an entire periphery thereof, for example, by rotary swaging, and therefore is positively contacted with a conductor portion of the wire.
The present application is based on Japanese Patent Application No. 2000-288529, which is incorporated herein by reference.
2. Description of the Related Art
FIG. 8 shows a related structure of connecting a wire to a terminal, and a pair of clamping piece portions 56, extending upright respectively from opposite side edges of a bottom plate portion of the terminal 50, are pressed to be fastened to a conductor portion 45 at an end portion of the wire 44 (from which a sheath is removed), thereby contacting the clamping piece portions 56 with the conductor portion 45.
The terminal 50 is a press-clamping terminal of a so-called open barrel-type which includes a round plate-like electrical contact portion 46 formed at one end thereof, the pair of conductor-clamping piece portions 56 (serving as a wire connection portion), and a pair of sheath clamping piece portions 43 provided rearwardly of the clamping piece portions 56. The sheath clamping piece portions 43, provided at the rear end of the terminal, increase the strength of fixing of the terminal 50 to the wire 44, and prevent the conductor portion 45 from being withdrawn from the terminal 50 even when a large pulling force acts on the terminal 50 and the wire 44.
FIG. 9 shows a method of connecting the terminal 50 and the wire 44 together. The pair of clamping piece portions 56 are pressed into a generally spectacles-shape between an upper crimper 47 and a lower anvil 48 (which jointly provide a clamping jig), so that wire elements of the conductor portion 45 are compressed between the pair of clamping piece portions 56 and the bottom plate portion 49.
However, in this connecting method (connecting structure) using the press-clamping terminal 50, the pair of clamping piece portions 56 extend upwardly from the opposite side edges of the bottom plate portion 49 at an abrupt angle close to a right angle, and therefore a gap between the wire connection portion and the conductor portion 45 is liable to develop at the boundary between each clamping piece portion 56 and the bottom plate portion 49, and the area of contact of the wire connection portion with the conductor portion 45 is reduced, and the electrical resistance increases.
And besides, the pair of clamping piece portions 56 are curled inwardly from the opposite sides, and therefore the clamping width S of the terminal 50 is larger as compared with the clamping height H thereof, and in the case where a plurality of terminals 50 are received in a connector housing, made of a synthetic resin, in a juxtaposed manner, there has been encountered a problem that the width of each terminal receiving chamber and hence the overall width of the connector (including the connector housing and the terminals 50) increases. Furthermore, the sheath clamping piece portions 43 (FIG. 8) must be provided in order to increase the strength of fixing of the terminal 50 to the conductor 45, and this has invited a problem that the structure is complicated. There has been encountered a further problem that it is rather difficult to use this terminal for a wire of a large diameter since the area of contact of the clamping piece portions 56 with the conductor 45 is small.
On the other hand, as shown in FIG. 10, a so-called closed barrel-type terminal 51 for pressing a conduction portion at regions, spaced at equal intervals in the peripheral direction, has been used particularly for a wire 54 of a large diameter. This terminal 51 includes an electrical contact portion 52 of a tubular shape formed at one end thereof, and a wire connection portion 53 of a tubular shape at the other end thereof. A conductor portion at an end portion of the wire 54, from which a sheath is removed, is inserted into the wire connection portion 53, and in this condition the wire connection portion 53 is pressed or compressed at regions, spaced at equal intervals in the circumferential direction, to be formed into a hexagonal shape. A mating male terminal (not shown) is inserted or threaded into the electrical contact portion (front portion) 52 to be connected thereto.
FIG. 11 shows one method of connecting this kind of terminal 51 to the wire 54 (see Examined Japanese Utility Model Publication No. Sho. 50-43746).
In this connecting method, the conductor 61 of the wire 54 is inserted into a cylindrical wire connection portion 62 of the terminal, and in this condition the wire connection portion 62 is pressed into a hexagonal shape by a pair of upper and lower dies 63, thereby intimately contacting the conductor portion 61 with the inner surface of the wire connection portion 62. Each of the dies 63 includes three pressing surfaces 64, and elongate projections 65 each formed on the corresponding pressing surface 64 and disposed centrally of the width thereof. Each elongate projection 65 presses widthwise a central portion of the corresponding side of the outer peripheral surface of the hexagonal wire connection portion 62 in a radial direction, thereby enhancing the contact of the wire conductor portion 61 with the wire connection portion 62 of the terminal.
However, there has been encountered a problem that the cost of the crimp terminal 51 of the closed barrel-type is higher than that of the press-clamping terminal 50 of the open barrel-type. And besides, in the connecting method of FIG. 11, when the wire connection portion 62 of the terminal is pressed or compressed by the pair of upper and lower dies 63, large pressing forces (internal stresses), directed toward the center (axis) of the conductor portion 61, are exerted while pressing forces (internal stresses), acting on the opposite (right and left) side portions of the wire connection portion, are liable to be reduced. As a result, there have been possibilities that interstices or gaps are liable to develop in a bundle of wire elements of the conductor portion 61 at the opposite side portions of the wire connection portion 62 and that gaps are liable to develop between the conductor portion 61 and the wire connection portion 62. When such gaps develop, there is a possibility that the electrical resistance increases, so that the energizing efficiency is lowered, and also the connected portions are heated.
And besides, burrs 68 are liable to develop at the opposite (right and left) sides of the wire connection portion 62 at regions between the upper and lower dies 63, and this detracts from the appearance of the wire connection portion 62, and in addition the width of the wire connection portion 62 increases, and therefore much time and labor have been required for removing these burrs so as to avoid such disadvantages.
In the case where the elongate projections 65, formed on the dies 63 (FIG. 11), are relatively large in size, the cross-section of the wire conductor portion 61 is deformed into a generally polygonal shape since the elongate projections 65 press the conductor portion 61 in the radial direction at the six regions. As a result, a concentrated stress develops at each convex portion 67 of the wire connection portion 62 disposed between any two adjacent concave portions 66 thereof formed by the elongate projections 65, so that the pressing of the conductor portion 61 is not uniform over the entire periphery thereof. Therefore, there have been possibilities that interstices or gaps are liable to develop in the conductor portion 61 (that is, in the bundle of wire elements thereof) and that gaps are liable to develop between the conductor portion 61 and the wire connection portion 62 of the terminal.